In an existing heat pump water heater, because the heating capacity of a heat pump system is relatively small, and the heating capacity decays at a low ambient temperature, an auxiliary electric heater is generally added for heating. Generally speaking, the heating rate of the electric heater is faster, while the heating rate of the heat pump system is slower; meanwhile, the heating efficiency of the electric heater is lower, while the heating efficiency of the electric heater is higher. In this case, it is particularly important to select which heat source at what time for heating to meet the hot water demand and energy saving demand of a user.
The existing thermal storage type water heater is generally started according to the temperature difference between a water temperature in a water tank and a set water temperature as a starting condition, in general, when the water temperature in the water tank is close to the set water temperature, the heat pump system is selected for heating to improve the heating energy efficiency; when the temperature difference between the water temperature in the water tank and the set water temperature is relatively large, the electric heater is selected for heating to shorten the heating time. The reduction of the water temperature in the water tank may be caused by water consumption of the user and may also be caused by natural heat dissipation of water in the water tank, therefore if the condition is used as the startup condition of the heat pump water heater, the water consumption condition of the user cannot be well reflected, and thus the heating source cannot be reasonably selected according to the water consumption condition of the user.